As disclosed in Japanese Patent No. 4837777, a hygrometer is known in which the humidity within a measurement space can be measured using a heat transfer section such as, for example, a heat pipe arranged across the measurement space and an outside space partitioned from each other by a thermal insulation section.
As an improvement of the hygrometer, the applicant of the present application has proposed a hygrometer below (see Japanese Patent Laid-open No. 2012-083206).
Specifically, with the hygrometer disclosed in Japanese Patent Application Laid-open No. 2012-083206, the humidity of a measurement space is obtained by computation from the temperature of a heat transfer section, the temperature of the measurement space, and the temperature of an outside space that are detected in a state where dew formation has been generated in a portion, of the heat transfer section, located within the measurement space.
In the hygrometer disclosed in Japanese Patent Application Laid-open No. 2012-083206, the temperature of the outside space is used in computation upon obtaining the humidity of the measurement space. Therefore, even if the humidity of the measurement space is constant, there are cases where the humidity (value of humidity) obtained by the hygrometer fluctuates due to fluctuation in the detected temperature of the outside space.